Diffusion and Sorption in Ethylene-Propylene Copolymers: Comparison of Experimental Methods

Abstract

The solubility and diffusion coefficients of various solvents in ethylene-propylene copolymers with different ethylene contents were measured over a temperature range of 30-200 °C using capillary column inverse gas chromatography and gravimetric sorption. The value of the Flory-Huggins parameter decreased with an increase in temperature. The infinitely dilute diffusion coefficients obtained by the two methods were consistent with each other. The data indicate that the diffusion coefficients and solubility parameters are independent of the ethylene content of the copolymers. The results obtained from the sorption technique were extrapolated using a free-volume theory to the limit of zero solvent concentration, and the free-volume model was used to interpret the diffusion data. Analysis of the diffusion data indicated that the inclusion of an activation energy in the free-volume model does not significantly improve the correlation of the diffusion data.

Inverse Gas Chromatography

“…Faridi et al [62] demonstrated the validity of IGC in comparison with gravimetric sorption methods. These experiments might be carried out at finite concentration and infinite dilution.…”

Peer Reviewed: Characterizing Polymers by MPC

“…Other investigators took advantage of the unique properties of fused-silica capillary columns using Equation 1 with a shape factor of 2/3, and Laurence derived a version of Equation 2 for capillary columns (25)(26)(27). Danner and co-workers (9,28) have used this technique to evaluate the free-volume model of polymers with D data measured by chromatographic methods over a range of temperatures encompassing T Although this approach is theoretically sound, it is extremely difficult to achieve the necessary experimental conditions with glassy polymeric liquids in which only a single mechanism (diffusion in the polymer) controls the second moment and only one mechanism (partition) determines the first moment. The first and second moments must be accurately determined to calculate D , as indicated by Equation 2.…”

Origin of Chemical Composition of Ethylene/Propylene Copolymer Produced with Ziegler–Natta Catalyst

“…Moreover, states of active sites vary in the course of polymerization due to interaction/reactions with alkylaluminum activator and donors . Most of previous researches have assumed that states of active sites mainly affect the chemical composition and its distribution of produced copolymer . Kakugo et al studied the influence of the amount of an external donor on the chemical composition distribution of ethylene/propylene copolymer .…”